Historically, electrical muscle stimulation has been employed to re-educate and re-train impaired muscles. The restoration of movement, especially in stroke paralysis, has seen limited success with what is known as functional electrical stimulation. The goal of functional electrical muscle stimulation is to restore functional capacity of muscles following a debilitating trauma. Primary candidates for functional electrical muscle stimulation include persons with paraplegia, hemiplegia and quadriplegia, as well as individuals with spinal cord injury or patients suffering from an impairment of the central nervous system, e.g., multiple sclerosis, head injury, or cerebral palsy.
U.S. Pat. No. 3,083,712 to Keegan relates generally to electrical muscle therapy, and more specifically to a programmed sequence for muscle therapy. It is an object of Keegan to provide an apparatus for producing sequential programming between antagonistic muscles in a proper time relation required for normal function of the muscles. In the illustrative example of Keegan, stimulation through an electrode is applied to the peroneal nerve, which causes muscle causes dorsiflexion and a slight eversion, i.e., turning out of the foot. In this example, the electrical stimulation is provided to assure that the toes of a foot will be lifted while the foot is being swung forward to avoid the dragging of the toes, dragging the toes being at the paralyzed side of the body while walking being characteristic of hemiplegics. The stimulation of the example is provided when a switch is depressed as the heel strikes the ground, thereby bridging contacts to provide energy from a battery source. Accordingly, the “sequential programming” of Keegan relates to a method for stimulating the peroneal nerve, not stimulating multiple muscles in a sequence. The functional movements caused, if at all, by this type of stimulation rarely become voluntary movements for the patient.
The ultimate goal for patients with spinal cord injury is to ambulate. Accordingly, muscles may be stimulated in the swing phase by electrical stimulation to advance the limb through its range of motion. Muscles are also stimulated during the stance phase so the patient can remain in the upright position. Despite the momentary recovery periods between swing and stance phases of a limb, fatigue sets in rapidly and muscles can simply fail due to the electrical stimulation's activation of fatigue-prone fast motor units. Fatigue may also prevail because disruptions of the spinal cord promote the conversion of slow fatigue-resistant to fast-fatigable muscle fibers, particularly in the weight-bearing muscles that cross single joints. Further, postural instability during such stimulation may cause falls. This instability is related to the small number of muscles stimulated by such electrical stimulation as compared to the total number of muscles that would normally require stimulation to advance a limb through its range of motion.
Accordingly, attempts have been made to overcome muscle failure due to fatigability and due to conversion of slow-twitch to fast-twitch muscle while a limb advances through its range of motion. U.S. Pat. No. 4,165,750 to Aleev et al. relates to a bioelectrically controlled electric stimulator of human muscles comprising an oscillator and a group of stimulator channels. Aleev uses a live person and functional electrical stimulation to improve the correspondence between movements actually performed by a human and programmed movements, to mitigate pain in the course of stimulation, and to make it possible to check the fatigability of muscles in the course of electric stimulation by changing the stimulation conditions at the onset of fatiguability. Aleev attempts to achieve these objects in a system that senses the bioelectric activity of the muscles of a programmer, manipulates the corresponding electric signal, and applies it to the muscles of a person whose movements are under control, all while continuing to sense the bioelectric activity of the muscles of the programmer. These objects are meant not only to restore the strength of damaged muscles, but also to restore lost motor skills, i.e. to enable a person to perform compound motions of the extremities, torso and head similar to those of a healthy person's extremities, torso and head. U.S. Pat. No. 5,350,415 to Cywinski relates to a device for trophic stimulation of muscles that does not depend on muscle contraction to achieve a therapeutic result. The device of Cywinski contains a pulse generation circuit that mimics the motor unit action potentials (MUAPs) that are naturally generated when muscles are innervated. MUAPs are known to have a mean rate of firing between 5 and 15 pulses per second, which is far below the stimulation rate necessary to achieve fused and forceful contraction of muscle. An object of Cywinski is to stimulate a trophic change of muscle contractile properties from fast-fatiguing into slow fatigue resistant types. Accordingly, Cwyinski achieves this therapeutic result without causing fused and forceful contraction of a muscle.
Electrical stimulation can be patterned after the body's natural movements and is hereinafter referred to as “patterned electrical muscle stimulation. Patterned electrical muscle stimulation applies a template of the firing pattern recorded in a healthy limb as it moves through its range of motion. Patterned electrical muscle stimulation may also be patterned after the body's natural MUAPs or any other observable sequencing of muscles. For example, the intact biceps and the triceps muscles' activity pattern may be detected in the form of electromyographic output and recorded during the flexion of the straight arm. Then, the timing and amplitude parameters of these electromyographic activities (the synergy patterns) are analyzed. Using a mathematical model, the activity patterns are reconstructed and applied via an electrical muscle stimulator to the impaired muscle pair. When impaired muscles contract, a sensory stimulus pattern ascends to the brain where, in a way thus far unidentified, a new motor template is generated. Once the new motor template is available, voluntary functional movement may become possible.
The methods discussed above relate primarily to the treatment of impaired muscles. More recently, researchers are studying the physiological processes for bioelectrical interactions among, and the activity regarding the growth and repair of, certain tissues and cells other than muscles. For example, osteoarthritis, also known as degenerative joint disease, is characterized by degeneration of articular cartilage, as well as proliferation and remodeling of subchondral bone. The usual symptoms of osteoarthritis are stiffness, limitation of motion, and pain. Osteoarthritis most commonly affects the knee joint more so than any other articular joint. Articular joints are encapsulated in a protective sac-like structure called a bursa, and there is a lining of the joint called the synovium that produces synovial fluid. This synovial fluid bathes and lubricates the articular surfaces of the joints and helps protect the cartilage. Synoviocytes and other cells found in the joint spaces adjacent to cartilage also have an important role in cartilage metabolism, e.g., synoviocytes produce metalloproteinases that are capable of breaking-down cartilage.
The breakdown of cartilage that is seen in conditions of osteoarthritis occurs in several stages. First, the synovial fluid becomes thinner and loses its elasticity and viscosity, which decreases its ability to cushion the joint. Without this cushioning effect, the cartilage in the joint may be more likely to “wear down.” Therefore, the surface of the smooth cartilage covering the joint softens and begins to lose its ability to absorb the impact of movement and can be more easily damaged from excess use or shock. The joint may also lose its shape as the cartilage breaks down, and bony growth or bone spurs may form on the edges of the affected joint compartment. As a result, small particles of bone and cartilage may degrade and begin to float around in the joint space, which contributes to the further degradation of the affected joint. Thus, one factor for measuring the effectiveness of methods of treatment for osteoarthritis may be the quantitative and qualitative analyses for measuring the viscosity and density of synovial fluid.
While some clinical studies have shown electrical muscle stimulation to reduce joint pain, the actual effectiveness of electrical muscle stimulation in reducing or reversing joint deterioration has been questioned based on the efficacy criteria used in such studies.
Thus, there is a need to demonstrate through the measurement of better efficacy criteria and actual physical indicia that patterned muscle stimulation has a beneficial effect on degenerative joint disease and osteoarthritis.